I did my last period on the 15th of December and started having sex on…

I did my last period on the 15th of December and started having sex on the 18th of December. I did a urine pregnancy test and was positive. Visited hospital days after and blood test confirmed positive but the scan shows nothing apart from the confirmation that am pregnant. I tried to abstain from sex since then but had sex yesterday morning and all symptoms of being pregnant are gone. I can't feel anything again. Is it something to be worried about or it's normal?